Gary, try replacing one or other of the parts if separate, ie' the gauge itself or the power unit / solar panel, mine are separate and replacing one or the other usually fixes it, you could also try the "reset" on the weather station and rescan for it.

Note: WMR88 rain gauge has been replaced by WMR89 - if you intend to change it or upgrade check the version of OS in it is the same or compatible with your sensor / weather station

Looks like it's $32 on the web site, must still be much cheaper than a full weather station though, mine cost around $300, does the red led on the power unit / solar panel come on every few minutes? did you try resetting the weather station?